Electronic surveillance measurement (ESM) receivers commonly require that frequency calculations be performed on a received signal from targets of interest. The frequency of an input signal is often measured using an instantaneous frequency measurement (IFM) receiver. The IFM receiver, generally, uses a difference in phase between a delayed and a non-delayed version of an input signal to calculate the frequency of the input signal.
The IFM receiver may cover a wide input frequency range such as, for example, in the range from 2 GHz to 18 GHz. The receiver may process short pulse widths with decent frequency accuracy. A conventional IFM receiver may be built through analog means with frequency correlators. The advancement in digital signal processing techniques has resulted in IFM receiver approaches with a one bit digitized signal. An example of an IFM receiver with a one bit digitized signal is disclosed in U.S. patent application Ser. No. 11/170,121, filed on Jun. 29, 2005, which is incorporated herein by reference in its entirety for its teachings on instantaneous frequency measurements.
It is important to be able to confirm the measurement of frequency of an IFM receiver. Presently, IFM receivers do not do this directly, but rather, try to detect a variety of conditions that could lead to an incorrect measurement.
A continuing need exists for an improved instantaneous frequency measurement (IFM) receiver. In particular, a need exists for directly confirming the measurement result of an IFM receiver that is more reliable than existing techniques currently in use.